Spin-torque memory with unidirectional write scheme

ABSTRACT

Spin torque magnetic memory elements that have a pinned layer, two free layers, and a current-blocking insulating layer proximate to at least one of the free layers. The resistive state (e.g., low resistance or high resistance) of the memory elements is altered by passing electric current through the element in one direction. In other words, to change from a low resistance to a high resistance, the direction of electric current is the same as to change from a high resistance to a low resistance. The elements have a unidirectional write scheme.

BACKGROUND

Spin electronics combine semiconductor technology and magnetics, and isa more recent development in memory devices, e.g., MRAM devices. In spinelectronics, the spin of an electron, rather than the charge, is used toindicate the presence of digital information. The digital information ordata, represented as a “0” or “1”, is storable in the alignment ofmagnetic moments within a magnetic element. The resistance of themagnetic element depends on the moment's alignment or orientation. Thestored state is read from the element by detecting the component'sresistive state.

The magnetic element, in general, includes a pinned layer and a freelayer, each having a magnetization orientation. The magnetizationorientations of the free layer and the pinned layer, define theresistance of the overall magnetic element. When the magnetizationorientations of the free layer and pinned layer are parallel, theresistance of the element is low. When the magnetization orientations ofthe free layer and the pinned layer are antiparallel, the resistance ofthe element is high. In order to sense the resistance of the magneticelement, current is driven through the magnetic element, either ascurrent in plane (“CIP”) or current perpendicular to the plane (“CPP”).

A typically memory array is formed from a plurality of memory cells,each which has a magnetic memory element and a select device such astransistor. In order to write to a conventional memory cell, a writecurrent is applied to a bit line while a read current is not applied. Inaddition, a write line carries a current to write to the selected memorycell. The combination of the current in the write line and the currentin the bit line generates a magnetic field large enough to switch thedirection or orientation of magnetization of the free layer of themagnetic element and thus write to the desired conventional memory cell.Depending upon the data written to the memory cell, the element, e.g.,magnetic tunneling junction, will have a high resistance or a lowresistance. To read from the memory cell, a read current is appliedinstead and the output voltage across the cell is read.

Although the conventional magnetic memory using the conventional spintunneling junctions can function adequately, there are barriers to theuse of the conventional magnetic elements and the conventional magneticmemory at higher memory cell densities. For example, a conventionalmemory array is written using an external magnetic field generated bycurrents driven through the bit line and the write line. Thus, themagnetization orientation of the free layer is switched by the externalmagnetic field generated by the current driven through the bit line andthe write line. The magnetic field required to switch the magnetizationorientation of the free layer, known as the switching field, isinversely proportional to the width of the magnetic element. As aresult, the switching field increases with smaller magnetic elements.Because the switching field is higher, the current required increases.This large current can cause various problems. For example, cross talkand power consumption increases. The driving circuits required to drivethe current that generates the switching field increases in area andcomplexity. Additionally, the write currents have to be large enough toswitch a magnetic memory cell but not so large that the neighboringcells are inadvertently switched. This upper limit on the write currentcan lead to writeability issues because the cells that are harder toswitch than others (due to fabrication and material nonuniformity) mayfail to write consistently.

What is needed are magnetic memory elements which can be used in amemory array of high density, low power consumption, low cross talk, andhigh reliability, while providing sufficient read signal. The presentdisclosure provides such improved magnetic memory elements.

BRIEF SUMMARY

The present disclosure relates to spin torque magnetic memory elementshaving a pinned layer and two free layers. Memory elements of thisdisclosure include a current-blocking insulating layer proximate to atleast one of the free layers. Additionally, the resistive state (e.g.,low resistance or high resistance) of the memory cells or memoryelements of this disclosure is altered by passing electric currentthrough the element in one direction. In other words, to change from alow resistance to a high resistance, the direction of electric currentis the same as to change from a high resistance to a low resistance. Theelements have a unidirectional write scheme.

A first particular embodiment of this disclosure is to a magneticelement having a first ferromagnetic free layer having a magnetizationorientation, a second ferromagnetic free layer having a magnetizationorientation, and a nonmagnetic metallic spacer layer therebetween. Acurrent-blocking insulator layer having a via therethrough is alsopresent. The magnetic element also includes a ferromagnetic pinned layerhaving a magnetization orientation pinned in a first direction and aninsulative barrier layer between the pinned layer and the first freelayer. The magnetic element is configured to allow the magnetizationorientation of the second free layer to change direction due to spintorque when a write current is passed through the via in thecurrent-blocking insulator layer. The magnetic element is alsoconfigured to allow the magnetization orientation of the first freelayer to change direction due to interlayer coupling with the secondfree layer when the write current is removed. In some embodiments, priorto passing the write current through the via, the magnetizationorientation of the second free layer is in the first direction and themagnetization orientation of the second free layer is in a seconddirection opposite to the first direction.

Another particular embodiment of this disclosure is to a magneticelement having a first ferromagnetic free layer having a magnetizationorientation, a second ferromagnetic free layer having a magnetizationorientation, and a nonmagnetic metallic spacer layer therebetween. Themagnetic element includes a current-blocking insulator layer having avia therethrough. Also present is a ferromagnetic pinned layer having amagnetization orientation pinned in a first direction and an insulativebarrier layer between the pinned layer and the first free layer. Priorto passing a write current through the magnetic element, themagnetization orientation of the first free layer is in the firstdirection and the magnetization orientation of the second free layer isin a second direction opposite to the first direction, but after passinga write current through the magnetic element, the magnetizationorientation of the second free layer is in the first direction and themagnetization orientation of the first free layer is in the seconddirection.

In another particular embodiment, the magnetic element is configured toallow the magnetization orientation of the second free layer to changedirection due to spin torque when a write current greater than acritical current is passed through the via in the current-blockinginsulator layer, and to allow the magnetization orientation of the firstfree layer to change direction due to interlayer coupling with thesecond free layer. Removal of the write current changes themagnetization orientation.

Another particular embodiment of this disclosure is a method of alteringthe resistance of a memory cell or memory element. This method includesproviding a magnetic element having a low resistance, the magneticelement comprising a first ferromagnetic free layer, a secondferromagnetic free layer, and a nonmagnetic metallic spacer layertherebetween, a current-blocking insulator layer between the first freelayer and the second free layer, the current-blocking insulator having avia therethrough, a ferromagnetic pinned layer, and an insulativebarrier layer between the pinned layer and the first free layer. Themagnetization orientation of the second free layer is switched bypassing a current in the second free layer through the via into thefirst free layer and the pinned layer, and the magnetization orientationof the first free layer is switched by removing the current from thesecond free layer. Thus is obtained a high resistance across themagnetic element. To switch the resistance back to a low resistance, themagnetization orientation of the second free layer is switched bypassing a current in the second free layer through the via into thefirst free layer and the pinned layer, and switching the magnetizationorientation of the first free layer by removing the current from thesecond free layer.

These and various other features and advantages will be apparent fromthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a first embodiment of a memory elementaccording to the present disclosure.

FIGS. 2A through 2D are schematic diagrams of a memory element accordingto the present disclosure during a write process having the current passthrough in a first direction. FIGS. 2E through 2H are schematic diagramsof the memory element during a second write process having the currentpass through in the same direction.

FIG. 3 is a schematic diagram of a second embodiment of a memory elementaccording to the present disclosure.

FIG. 4 is a schematic diagram of a third embodiment of a memory elementaccording to the present disclosure.

FIG. 5 is a schematic diagram of a fourth embodiment of a memory elementaccording to the present disclosure.

FIG. 6 is a schematic diagram of a fifth embodiment of a memory elementaccording to the present disclosure.

FIG. 7 is a schematic diagram of a sixth embodiment of a memory elementaccording to the present disclosure, this embodiment having multiplevias.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying setof drawings that form a part hereof and in which are shown by way ofillustration several specific embodiments. It is to be understood thatother embodiments are contemplated and may be made without departingfrom the scope or spirit of the present invention. The followingdetailed description, therefore, is not to be taken in a limiting sense.While the present invention is not so limited, an appreciation ofvarious aspects of the invention will be gained through a discussion ofthe examples provided below.

Referring to FIG. 1, an embodiment of a magnetic memory element 10 inaccordance with the present disclosure is schematically anddiagrammatically illustrated. Although magnetic memory element 10 isillustrated as two dimensional, it should be understood that memoryelement 10 and others according to this disclosure are three-dimensional‘stacks’ or ‘towers’, for example, having a circular, elliptical, orrectangular (e.g., square) shape when viewed from the top. Although notillustrated herein, memory element 10 may be formed on a substrate, andmay be electrically connected to a bit line and a word line. Memoryelement 10 and other memory elements may include additional layers, suchas seed or capping layers, not depicted herein for clarity.

Memory element 10 includes an antiferromagnetic pinning layer 12, aferromagnetic pinned layer 14, a first ferromagnetic free layer 16 and asecond ferromagnetic free layer 18. Each of these layers, ferromagneticpinned layer 14, first ferromagnetic free layer 16 and secondferromagnetic free layer 18, has a magnetic orientation or magnetizationorientation associated therewith. Positioned between pinned layer 14 andfirst ferromagnetic free layer 16 is a barrier layer 15. Additionally,positioned between first ferromagnetic free layer 16 and secondferromagnetic free layer 18 is a nonmagnetic (metallic) spacer layer 17.Memory element 10 and its various layers (e.g., pinning layer 12, pinnedlayer 14, barrier layer 15, free layers 16, 18, etc.) can be made byconventional thin film processing techniques, including lithography orvapor deposition.

Memory element 10 can be considered to have a first magnetic element anda second magnetic element in series. The first element could beconsidered to include antiferromagnetic pinning layer 12, pinnedferromagnetic layer 14, first ferromagnetic free layer 16, and barrierlayer 15. Barrier layer 15 allows electrons to tunnel therethroughbetween pinned layer 14 and free layer 16. The second element could beconsidered to include the first ferromagnetic layer 16, secondferromagnetic layer 18, and nonmagnetic spacer 17. In accordance withthe invention of this disclosure, it is the first magnetic element thatcontributes the majority of the resistance across cell 10.

Magnetic memory elements of this disclosure include a current-blockinginsulating layer proximate the exposed free layer. For memory element10, positioned between metallic spacer 17 and second free layer 18 is aninsulator layer 20 having a via 25 therein. Insulator layer 20 and othercurrent-blocking layers can be made by conventional thin film processingtechniques, including lithography or vapor deposition. Insulator layer20 is insulative or blocking to electrons (i.e., current) passingtherethrough. Current, or electrons, which would pass through themagnetic element in a CPP configuration, can only pass through via 25 ininsulator layer 20. Via 25 may be circular, elliptical, or have anyother suitable shape defined by insulator layer 20, or via 25 may extendfrom one edge of insulator layer 20 to the other, thus forming at leasttwo separate and distinct parts of layer 20.

FIGS. 2A through 2D illustrate the altering of the magnetizationorientation of the free layers 16, 18 in memory element 10 when acurrent is applied. This altering of the magnetization orientationswitches the resistance state of memory element 10, for example, from afirst resistance state (e.g., a low resistance state (R_(L))) to asecond resistance state (e.g., a high resistance state (R_(H))).

The assumption is made that free layers 16, 18 are antiferromagneticallycoupled to each other, and that the coercivity of second free layer 18and the interlayer coupling field are larger than the coercivity offirst free layer 16.

Since the magnetic tunneling junction contributes the majority of theresistance across cell 10 and the magnetoresistance ratio of the cell,the resistance of the cell is determined, in large part, by themagnetization orientation of first free layer 16 and pinned layer 14.Because pinned layer 14 has its magnetization orientation fixed, changein the magnetization orientation of first free layer 16 will change theresistance and the logic bit state of memory element 10.

FIG. 1 illustrates memory element 10 at an initial, equilibrium state,with no electric current having been passed through. First free layer 16is parallel to pinned layer 14, and first free layer 16 is antiparallelto second free layer 18. In this configuration, cell 10 is at firstresistance state (e.g., a low resistance state (R_(L))), due to theparallel magnetization orientation of pinned layer 14 and first freelayer 16.

To switch the magnetization orientation of second free layer 18 usingspin transfer, an electric current “I” is applied from second free layer18 to first free layer 16 and through cell 10; see FIG. 2A. This currentis driven from second free layer 18 through via 25 to first free layer16 to pinned layer 14.

When current is driven from second free layer 18 through first freelayer 16 to pinned layer 14, conduction electrons travel the reversedirection from pinned layer 14 to first free layer 16 to second freelayer 18. The majority of electrons traveling from pinned layer 14 havetheir spins polarized in the same direction as the magnetizationorientation of pinned layer 14. These electrons interact with themagnetic moments of second free layer 18 near the interface betweensecond free layer 18 and the spacer layer 17. As a result of thisinteraction, the electrons transfer their spin angular momentum tosecond free layer 18. Thus, angular momentum corresponding to spinsantiparallel to the magnetization orientation of second free layer 18(and parallel to pinned layer 14 and to first free layer 16) istransferred to second free layer 18. When sufficient angular momentum istransferred by the electrons, the magnetization orientation of secondfree layer 18 is switched to be parallel to the magnetizationorientation of pinned layer 14 and first free layer 16. Thismagnetization orientation dynamics occurs in second free layer 18 viaexchange coupling.

Memory element 10, however, includes insulator layer 20 between firstfree layer 16 and second free layer 18 which does not allow current orelectrons to pass therethrough except through via 25. The electrondensity and thus the spin torque within second free layer 18 are highestproximate via 25. Consequently, the magnetization orientation of secondfree layer 18 proximate via 25 switches before other areas of secondfree layer 18. See FIG. 2B.

After the area of second free layer 18 proximate via 25 has switched,the magnetization orientation of the entire second free layer 18switches. After this switch, second free layer 18 is parallel with firstfree layer 16; see FIG. 2C. After the current is removed (FIG. 2C) toend the write process, the parallel configuration of first free layer 16in relation to second free layer 18 is not energetically favored, andthe interlayer coupling forces the first free layer 16 magnetizationorientation to switch, resulting in an antiparallel orientation (FIG.2D). At this configuration, memory element 10 is at a second resistancestate (e.g., a high resistance state (R_(H))), due to the due to theantiparallel magnetization orientation of pinned layer 14 and first freelayer 16.

As seen in FIGS. 2A through 2C, the magnetization orientation of firstfree layer 16 does not switch due to the application of current “I”.This is due to the limited passage between first free layer 16 to secondfree layer 18, i.e., via 25. Due to the presence of insulator layer 20,the current fans out from via 25 into first free layer 16, resulting ina current density passing through first free layer 16 that is lower thanthe critical current density for switching first free layer 16.

To switch memory element 10 back a low resistance state (R_(L)), anelectric current is applied in the same direction as the write currentthat switched the resistance to the high state (R_(H)); see FIGS. 2Ethrough 2H. The magnetization orientations of first free layer 16 andsecond free layer 18 will experience similar dynamics as when the writecurrent was applied. The magnetization orientation of first free layer16 and second free layer 18 will switch back to their initial direction,in essentially the same manner as described above.

For the memory elements in accordance with this disclosure, the writecurrent is applied in a single direction. Free layers 16, 18 changetheir magnetization orientations regardless the initial state.Therefore, prior to writing data in magnetic memory element 10, itsstate should be confirmed by a read operation to determine whether ornot a write operation is needed to change the state of the magneticmemory element. In some embodiments, the read operation is also calledpre-read operation.

The discussion above has been for a “write” operation, providing memoryelement 10 with either a low resistance state (R_(L)) or a highresistance state (R_(H)), which correlates with either a “0” or “1”. To“read” memory element 10, a current is applied through the stackstructure and the resistance of cell 10 is measured. This read currentis smaller than the write current, in order to not alter the resistanceof cell 10.

Various alternative configurations for memory elements having acurrent-blocking insulating layer proximate the exposed free layer areillustrated in FIGS. 3 through 7. The various layers of the memoryelements of FIGS. 3 through 7 have the same properties and qualities asthe respective layers of memory element 10, unless otherwise indicated.

FIG. 3 illustrates a memory element 30 having an antiferromagneticpinning layer 32, a ferromagnetic pinned layer 34, a first ferromagneticfree layer 36 and a second ferromagnetic free layer 38. Each of theselayers, ferromagnetic pinned layer 34, first ferromagnetic free layer 36and second ferromagnetic free layer 38, has a magnetic orientation ormagnetization orientation associated therewith; for clarity in thefigure, the magnetization orientation of second free layer 38 is notillustrated. Positioned between pinned layer 34 and first free layer 36is a barrier layer 35. Additionally, positioned between first free layer36 and second free layer 38 is a nonmagnetic (metallic) spacer layer 37.Positioned between metallic spacer 37 and second free layer 38 is aninsulator layer 40 having a via 45 therein. In memory element 30, via 45in insulator layer 40 has material from second free layer 38 therein,whereas in memory element 10, via 25 in insulator layer 20 has materialfrom metallic spacer 17 therein.

In cell 30, a portion of second free layer 38 is occupies the volume ofvia 45, the top surface of free layer 38 includes a depression 39therein. Such a depression 39 forms during the manufacturing process ofcell 30, when material from free layer 38 fills in via 45. Because ofdepression 39 in second free layer 38, the exchange coupling betweenmagnetic moments is weak at that region. Because of this, the writecurrent density to switch the center part of second free layer 3 8 islower since the exchange coupling of the magnetic moments influences thewrite current density. After the portion of free layer 38 proximate via45 (e.g., the center part) is switched, the remainder of second freelayer 38 will be switched by the exchange coupling.

Because of the limited passage area between first free layer 36 tosecond free layer 38, due to the present of insulator layer 40, whichdoes not allow electrons to pass therethrough except through via 45, thecurrent fans out from via 45 into first free layer 36 so that thedensity of the current passing through first free layer 36 is lower thanthe critical current density for switching first free layer 36. Thecurrent density and thus the spin torque within second free layer 38 arehighest proximate via 45. Consequently, the magnetization orientation ofsecond free layer 38 proximate via 45 switches before other areas ofsecond free layer 38.

Another embodiment is illustrated in FIG. 4 where a memory element 50includes an antiferromagnetic pinning layer 52, a ferromagnetic pinnedlayer 54, a first ferromagnetic free layer 56 and a second ferromagneticfree layer 58. Positioned between pinned layer 54 and first free layer56 is a barrier layer 55. Additionally, positioned between first freelayer 56 and second free layer 58 is a nonmagnetic (metallic) spacerlayer 57. Positioned adjacent second free layer 58 is an insulator layer60 having a via 65 therein.

In this embodiment, because of the limited passage area into second freelayer 58 for a write current, due to the present of insulator layer 60that does not allow electrons to pass therethrough except through via65, the current fans out from via 65 into second free layer 58 so thatthe density of the current passing through second free layer 58 is lowerthan the critical current density for switching second free layer 58.The current density and thus the spin torque within second free layer 58are highest proximate via 68. Consequently, the magnetizationorientation of second free layer 58 proximate via 65 switches beforeother areas of second free layer 58.

A third alternative embodiment is illustrated in FIG. 5 as a memoryelement 70 that includes an antiferromagnetic pinning layer 72, aferromagnetic pinned layer 74, a first ferromagnetic free layer 76 and asecond ferromagnetic free layer 78. Positioned between pinned layer 74and first free layer 76 is a barrier layer 75 and positioned betweenfirst free layer 76 and second ferromagnetic free layer 78 is anonmagnetic (metallic) spacer layer 77. Present within second free layer78 is an insulator layer 80 having a via 85 therein.

Similar to memory elements 10, 30, because of the limited passage areabetween first free layer 76 and second free layer 78 for a current topass through, the current fans out from via 85 into second free layer 88so that the current density and spin torque within second free layer 78are highest proximate via 85. Consequently, the magnetizationorientation of second free layer 78 proximate via 85 switches beforeother areas of second free layer 78.

FIG. 6 illustrates a memory element 90 having an antiferromagneticpinning layer 92, a ferromagnetic pinned layer 94, a first ferromagneticfree layer 96 and a second ferromagnetic free layer 98. Positionedbetween pinned layer 94 and first free layer 96 is a barrier layer 95and positioned between first free layer 96 and second free layer 98 is anonmagnetic (metallic) spacer layer 97. Memory element 90 includes aninsulator layer 100, a portion 102 of which is positioned between spacerlayer 97 and second free layer 98. In this embodiment, another portion104 of insulator layer 100 extends through second free layer 98, fromspacer layer 97 to an exposed top surface of memory element 90. Portion104 defines a passage or via 105 within second free layer 98. If viewedfrom the top, one would see that second free layer 98 has a continuous(e.g., annular) perimeter region and a central core (i.e., via 105)defined by portion 104 of insulator layer 100. The central core may becircular, elliptical, or other suitable shape.

The previous embodiments have had a single via through the insulativelayer. Also within the scope of this disclosure are memory elementshaving more than one via in the insulative layer through which thecurrent and electrons can pass. Referring to FIG. 7, a memory element110 is illustrated having three vias through the insulative layer.Specifically, memory element 110 has an antiferromagnetic pinning layer112, a ferromagnetic pinned layer 114, a first ferromagnetic free layer116 and a second ferromagnetic free layer 118. Positioned between pinnedlayer 114 and first free layer 116 is a barrier layer 115 and positionedbetween first free layer 116 and second free layer 118 is a nonmagnetic(metallic) spacer layer 117. An insulator layer 120 is positionedbetween spacer layer 117 and second free layer 118, similar to theposition of insulator layer 20 in memory element 10. Insulator layer 120has a plurality of vias 125 therethrough; in this particular embodiment,three vias 125.

For this memory element 110, current fans out from the three vias 125into first free layer 116. Depending on the dimensions of vias 125 anddistance between them, the current through a first via 125 may overlapwith the current through a neighboring via 125. Because themagnetization orientation of second free layer 118 proximate vias 125switches before other areas of second free layer 118, three areas offree layer 118 will typically switch before the other four areas.

Thus, numerous embodiments of the SPIN-TORQUE MEMORY WITH UNIDIRECTIONALWRITE SCHEME are disclosed. The implementations described above andother implementations are within the scope of the following claims. Oneskilled in the art will appreciate that the present invention can bepracticed with embodiments other than those disclosed. The disclosedembodiments are presented for purposes of illustration and notlimitation, and the present invention is limited only by the claims thatfollow.

1. A magnetic element comprising: a first ferromagnetic free layer having a magnetization orientation, a second ferromagnetic free layer having a magnetization orientation, and a nonmagnetic metallic spacer layer therebetween; a ferromagnetic pinned layer having a magnetization orientation pinned in a first direction; an insulative barrier layer between the pinned layer and the first free layer; a current-blocking insulator layer proximate the second free layer, the current-blocking insulator having a via therethrough; wherein the magnetic element is configured to allow the magnetization orientation of the second free layer to change direction due to spin torque when a write current is passed through the via in the current-blocking insulator layer, and wherein the magnetic element is configured to allow the magnetization orientation of the first free layer to change direction due to spin torque when the write current is removed.
 2. The magnetic element of claim 1 wherein prior to passing the write current through the via, the magnetization orientation of the second free layer is in the first direction and the magnetization orientation of the second free layer is in a second direction opposite to the first direction.
 3. The magnetic element of claim 1 further comprising a pinning layer on a side of the pinned layer opposite the barrier layer.
 4. The magnetic element of claim 1 wherein the current-blocking insulator layer is between the first free layer and the second free layer.
 5. The magnetic element of claim 4 wherein the current-blocking insulator layer is between the metallic spacer layer and the second free layer.
 6. The magnetic element of claim 5, wherein the metallic spacer layer extends into the via.
 7. The magnetic element of claim 5, wherein the second free layer extends into the via.
 8. The magnetic element of claim 1, wherein the current-blocking insulator layer is within the second free layer.
 9. The magnetic element of claim 1, wherein the current-blocking insulator layer is on a surface of the second free layer opposite the metallic spacer layer.
 10. The magnetic element of claim 1, wherein the current-blocking insulator layer defines a perimeter region around the via.
 11. The magnetic element of claim 1, wherein the current-blocking insulating layer comprises a plurality of vias therethrough.
 12. The magnetic element of claim 1, further wherein: the magnetic element is configured to allow the magnetization orientation of the second free layer to change direction due to spin torque when a second write current is passed through the via in the same direction as the first write current after the first write current, and the magnetic element is configured to allow the magnetization orientation of the first free layer to change direction due to spin torque when the second write current is removed.
 13. A magnetic element comprising: a first ferromagnetic free layer having a magnetization orientation, a second ferromagnetic free layer having a magnetization orientation, and a nonmagnetic metallic spacer layer therebetween; a ferromagnetic pinned layer having a magnetization orientation pinned in a first direction; and an insulative barrier layer between the pinned layer and the first free layer; a current-blocking insulator layer proximate the second free layer, the current-blocking insulator having a via therethrough; wherein prior to passing a write current through the magnetic element, the magnetization orientation of the first free layer is in the first direction and the magnetization orientation of the second free layer is in a second direction opposite to the first direction, and wherein after passing a write current through the magnetic element, the magnetization orientation of the second free layer is in the first direction and the magnetization orientation of the first free layer is in the second direction.
 14. The magnetic element of claim 13 wherein the current-blocking insulator layer is between the first free layer and the second free layer.
 15. The magnetic element of claim 14 wherein the current-blocking insulator layer is between the metallic spacer layer and the second free layer.
 16. The magnetic element of claim 13, wherein the current-blocking insulator layer is within the second free layer.
 17. The magnetic element of claim 13, wherein the current-blocking insulator layer is on a surface of the second free layer opposite the metallic spacer layer.
 18. The magnetic element of claim 13, wherein the current-blocking insulator layer defines a perimeter region around the via.
 19. The magnetic element of claim 13, wherein the current-blocking insulating layer comprises a plurality of vias therethrough.
 20. The magnetic element of claim 13, further wherein: prior to passing a second write current through the magnetic element, the magnetization orientation of the first free layer is in the second direction and the magnetization orientation of the second free layer is in first direction, and wherein after passing the second write current through the magnetic element in the same direction as the first write current, the magnetization orientation of the second free layer is in the second direction and the magnetization orientation of the first free layer is in the first direction.
 21. A method of altering a resistance of a memory cell comprising: providing a magnetic element having a low resistance, the magnetic element comprising: a first ferromagnetic free layer having a magnetization orientation, a second ferromagnetic free layer having a magnetization orientation, and a nonmagnetic metallic spacer layer therebetween; a ferromagnetic pinned layer having a magnetization orientation pinned in a first direction; an insulative barrier layer between the pinned layer and the first free layer; and a current-blocking insulator layer proximate the second free layer, the current-blocking insulator having a via therethrough; switching the magnetization orientation of the second free layer by passing a current in the second free layer through the via into the first free layer and the pinned layer; and switching the magnetization orientation of the first free layer by removing the current from the second free layer, and obtaining a high resistance across the magnetic element.
 22. The method of claim 21 further including altering the high resistance across the magnetic element to a low resistance by: switching the magnetization orientation of the second free layer by passing a current in the second free layer through the via into the first free layer and the pinned layer; and switching the magnetization orientation of the first free layer by removing the current from the second free layer, and obtaining a low resistance across the magnetic element. 